Completion of a comparative study of the mechanical properties of human fluorotic and nonfluorotic cortical bone. The fluorotic specimens are obtained from the bones of a 45-year-old Punjab man who died with severe endemic fluorosis. The nonfluorotic specimens are oobtained from local osteological collections. The fracture surface of tensile, compressive, shearing, torsion and fatigue specimens will be examined by the scanning electron microscope for additional evidence of fracture mechanisms. Relations of the torsion properties of adult human cortical bone to its microscopic structure, as seen in the light and polarizing microscope, as well as degree and distribution of calcification, as seen by microradiography, will be undertaken. Torsion specimens of known mechanical properties are available for this study. Analysis of enlarged microradiographs and photomicrographs of cross sections of the specimens taken in ordinary and in polarized light will be made as in similar previous studies. Age, and possibly sexual differences in the microscopic structure of representative cross sections of intact bones will be initiated. Special techniques for the preparation and testing of very small cylinders (1/30,000 inch in diameter x 1/60,000 inch in length) of human cortical bone are being perfected. Mechanical property, histological, and microradiographic data will be analyzed for statistically significant differences and correlations.